Spider Body Size Research Articles

Landscape configuration, organic management, and within‐field position drive functional diversity of spiders and carabids

AbstractAgricultural management intensity and landscape heterogeneity act as the main drivers of biodiversity loss in agricultural landscapes while also determining ecosystem services. The trait‐based functional diversity approach offers a way to assess changes in community functionality across agroecosystems. We focused on carabids and spiders, because they are an important component of crop field biodiversity and have significant biological control potential.We assessed the effect of small‐ vs. large‐scale agricultural landscapes, organic farming, and within‐field position on functional diversity of spiders and carabids. We sampled pairs of organic and conventional winter wheat fields in small‐scale agricultural landscapes (former West Germany) and in neighbouring large‐scale agricultural landscapes (former East Germany). We sampled arthropods with funnel traps in transects at field edges, field interiors (15 m from edge), and field centres.The gradient from field edges towards the centres played an important role: spider body size decreased; ballooning ability increased, and hunting strategy switched from active hunters to more web‐builders—presumably, due to higher microhabitat stability in the field centre. Higher trait diversity of spiders in field edges suggested higher biocontrol potential in small‐scale agriculture. In contrast, carabid feeding switched from herbivores to carnivores, presumably due to higher pest densities inside crop fields. Furthermore, small‐scale agricultural landscapes and organic management supported larger, i.e., less dispersive carabids.Synthesis and applications. In our research, spiders were more sensitive to edge effects and less sensitive to management and landscape composition than carabids. Smaller fields and longer edges, as well as organic management increase carabid functional diversity, which may increase resilience to environmental change. Since many spider species are confined to field edges, the effect of within‐field position on functional diversity is more important in small‐scale agricultural landscapes with more edge habitat than in large‐scale agricultural landscapes. Our findings suggest that European Union policy should acknowledge the high benefits of small‐scale agriculture for the functional role of major predators such as spiders and carabid beetles, as the benefits are equal to those from a conversion to organic agriculture.

Coevolution of female and male genital components to avoid genital size mismatches in sexually dimorphic spiders.

BackgroundIn most animal groups, it is unclear how body size variation relates to genital size differences between the sexes. While most morphological features tend to scale with total somatic size, this does not necessarily hold for genitalia because divergent evolution in somatic size between the sexes would cause genital size mismatches. Theory predicts that the interplay of female-biased sexual size dimorphism (SSD) and sexual genital size dimorphism (SGD) should adhere to the ‘positive genital divergence’, the ‘constant genital divergence’, or the ‘negative genital divergence’ model, but these models remain largely untested. We test their validity in the spider family Nephilidae known for the highest degrees of SSD among terrestrial animals.ResultsThrough comparative analyses of sex-specific somatic and genital sizes, we first demonstrate that 99 of the 351 pairs of traits are phylogenetically correlated. Through factor analyses we then group these traits for MCMCglmm analyses that test broader correlation patterns, and these reveal significant correlations in 10 out of the 36 pairwise comparisons. Both types of analyses agree that female somatic and internal genital sizes evolve independently. While sizes of non-intromittent male genital parts coevolve with male body size, the size of the intromittent male genital parts is independent of the male somatic size. Instead, male intromittent genital size coevolves with female (external and, in part, internal) genital size. All analyses also agree that SGD and SSD evolve independently.ConclusionsInternal dimensions of female genitalia evolve independently of female body size in nephilid spiders, and similarly, male intromittent genital size evolves independently of the male body size. The size of the male intromittent organ (the embolus) and the sizes of female internal and external genital components thus seem to respond to selection against genital size mismatches. In accord with these interpretations, we reject the validity of the existing theoretical models of genital and somatic size dimorphism in spiders.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-016-0734-9) contains supplementary material, which is available to authorized users.

Multi-taxa trait and functional responses to physical disturbance.

Examining assemblage trait responses to environmental stressors extends our understanding beyond patterns of taxonomic diversity and composition, with results potentially transferable among bioregions. But the degree to which trait responses may be generalized across taxonomic groups remains incompletely understood. We compared trait responses among carabids, spiders and plants to an experimentally manipulated gradient of physical disturbance, replicated in open habitats within a forested landscape. Recolonization of recently disturbed habitats is expected to favour species with traits that promote greater dispersal ability, independent of taxa. We specifically predicted that physical disturbance would increase the representation of carabids with smaller body size, wings or wing dimorphism, spiders able to disperse aerially, and plants with therophyte life-history and wind-dispersed seed. We sampled 197 arthropod species (14,738 individuals) and 164 species of plant. The strength of association between each trait and the disturbance intensity was quantified by correlating matrices of species by traits, species abundance by sites and sites by environment, with significance assessed by comparison with a null model. Responses of biological traits varied among taxa but could be consistently interpreted in terms of dispersal ability. Trait shifts for carabid and plant assemblages were as predicted and correspond to those observed in other disturbance regimes. Assemblages after disturbance comprised smaller and winged carabids, and smaller plants with wind-dispersed seed, consistent with selection for species with better dispersal ability. In contrast, aerial dispersal did not appear important in spider recolonization, instead terrestrial dispersal ability was suggested by the increased abundance of larger-bodied and cursorial species. However, larger spider body size was also associated with an active-hunting strategy, also favoured in the post-disturbance environment. Trait-function linkage differed among taxa and was sometimes diffuse, with covariance among biological traits and the mapping of individual traits to multiple ecological functions. In particular, body size responses reflected correlations with life history, susceptibility to perturbation and dispersal ability that were inconsistent between the two arthropod groups. Selection of traits for assessment should therefore be taxa specific. Generalizations of trait responses across taxa should only be conducted where functional or ecological significance of assembly-level changes can be understood.

Disentangling the phylogenetic and ecological components of spider phenotypic variation.

An understanding of how the degree of phylogenetic relatedness influences the ecological similarity among species is crucial to inferring the mechanisms governing the assembly of communities. We evaluated the relative importance of spider phylogenetic relationships and ecological niche (plant morphological variables) to the variation in spider body size and shape by comparing spiders at different scales: (i) between bromeliads and dicot plants (i.e., habitat scale) and (ii) among bromeliads with distinct architectural features (i.e., microhabitat scale). We partitioned the interspecific variation in body size and shape into phylogenetic (that express trait values as expected by phylogenetic relationships among species) and ecological components (that express trait values independent of phylogenetic relationships). At the habitat scale, bromeliad spiders were larger and flatter than spiders associated with the surrounding dicots. At this scale, plant morphology sorted out close related spiders. Our results showed that spider flatness is phylogenetically clustered at the habitat scale, whereas it is phylogenetically overdispersed at the microhabitat scale, although phylogenic signal is present in both scales. Taken together, these results suggest that whereas at the habitat scale selective colonization affect spider body size and shape, at fine scales both selective colonization and adaptive evolution determine spider body shape. By partitioning the phylogenetic and ecological components of phenotypic variation, we were able to disentangle the evolutionary history of distinct spider traits and show that plant architecture plays a role in the evolution of spider body size and shape. We also discussed the relevance in considering multiple scales when studying phylogenetic community structure.

Scramble competition for moulting females as a driving force for extreme male dwarfism in spiders

Extreme sexual size dimorphism in spiders is generally assumed to result from female gigantism, male dwarfism or both. However, field evidence demonstrating the existence and nature of these driving mechanisms is still lacking. In this study we performed field monitoring and laboratory manipulations on the giant wood spider, Nephila pilipes, to assess pre- and postcopulatory sexual selection pressures on males. Results of field monitoring showed that females frequently changed web sites and travelled for long distances and consequently the advantage of large males in occupying favourable positions on webs did not guarantee them higher mating opportunities. Most of the mating events occurred during female moulting but there was typically only one male present on a female’s web, indicating a low level of precopulatory maleemale physical competition. Results of staged double-mating experiments using the sterile-male technique showed that sperm competition in N. pilipes followed a mixed-priority pattern. So males able to find a moulting female earlier than their rivals, to monopolize it to transfer more sperm, are favoured. Therefore, scramble competition for suitable but ephemeral penultimate-stage females is one major force driving protandry and maintaining small body size in spiders with extreme sexual dimorphism.

Sexual Selection in the Water Spider: Female Choice and Male-Male Competition

The water spider Argyroneta aquatica is the only spider spending its whole life under water, and one of the few spider species in which males are larger than females. Previous studies indicated that males can cannibalize females, which is uncommon among spiders. Here we aimed to further test for a potential influence of sexual selection on male body size. We examined the importance of female choice by testing whether females prefer the larger of two simultaneously presented males as mating partners. Further, we examined the influence of male–male competition by comparing the fighting behaviour between large and small males when alone or when together with a female, and we determined the outcome of fights. We found that females approach and choose large males as mating partners, despite the risk of male cannibalism. Additionally, males intensively compete for females, and large males clearly win against smaller ones. Hence sexual selection seems to be important for the evolution of the peculiar sexual size dimorphism of water spiders, as large size is beneficial for males in both the intra- and intersexual context. Previous studies have suggested an important role of natural selection in the sex-specific body size of water spiders, but natural and sexual selection mechanisms apparently work in the same direction, favouring large male size.

Flow regime alters body size but not the use of aquatic subsidies in a riparian predatory arthropod

AbstractAlterations to river flow conditions have wide impacts on riparian organisms in terms of behavior and biomass. However, little is known about natural flood impacts on prey use and individual growth of riparian predators. Using stable carbon isotope analysis, we investigated flood impacts on aquatic‐prey use and the size structure of an orb‐web spider, Nephila clavata, during 3 years under different flood conditions in a black locust forest in the middle reaches of the Chikuma River. Large floods depressed aquatic‐prey abundance, but did not affect terrestrial‐prey abundance in the riparian forest. Consequently, spider growth was stunted after large floods. Spider body size was positively correlated with the body sizes of both aquatic and terrestrial insects in spider webs, where terrestrial insects were significantly larger than aquatic insects. The δ13C of aquatic insects was about 8‰ higher than that of terrestrial insects, and the δ13C of both insect groups did not vary significantly between months or among years. A negative relationship was found between body size and δ13C in spiders under different subsidies levels. Our results showed that flow regime altered spider growth through changes in aquatic subsidies level, but not aquatic‐prey use by the spiders due to relative body sizes of predators and prey. Changes in relative body sizes of predator and prey may be an important factor in understanding nutrients, materials, and energy flows in aquatic and terrestrial linkages in the context of flow regime.

Impacts of temperature, hunger and reproductive condition on metabolic rates of flower-dwelling crab spiders (Araneae: Thomisidae)

Temperature strongly affects spider metabolic rate. Consequently, quantifying a species' temperature-metabolism relationship is useful in evaluating consequences of choices that affect body temperature. Body size also influences metabolic rate, and body size in spiders is strongly impacted by feeding and reproductive condition. Using adult female crab spiders, Misumenoides formosipes Walckenaer 1837 and Mecaphesa asperata (Hentz 1847) (formerly Misumenops asperatus) acclimated to field ambient conditions, I measured standard metabolic rates (SMR) over an ecologically relevant temperature range (10–40° C). I controlled hunger and reproductive condition of M. formosipes using starved (25 days post-feeding) or fed (7 days post-feeding) spiders, and virgin or mated spiders; in experiments with M. asperata, I used fed spiders of unknown reproductive status. Temperature strongly affected crab spider SMR, and both species showed similar temperature-SMR relationships. Mecaphesa asperata displayed equivalent temperature coefficients (Q10s – the factor by which a physiologic process changes with temperature) for SMR across the experimental temperature range, while M. formosipes had significantly higher Q10 at low temperature than at mid-range or high temperature; Q10s of the two species reflected previously determined impacts of temperature on hunting performance. Influence of hunger-reproductive condition on SMR of M. formosipes depended on how I accounted for body size; regardless of method, gravid spiders did not show elevated metabolic rate. Lastly, I combined crab spider SMR data with published SMR data to generate mass-metabolism equations for spiders; mass-scaling exponents approximated 0.67.

Relationships between physiological characteristics and trace metal body burdens of banded garden spiders Argiope trifasciata (Araneae, Araneidae)

Banded garden spiders ( Argiope trifasciata) were collected at the Ballona Wetlands, a metal contaminated salt marsh. The relationship between spider body size and individual metal loads was investigated. Biochemical markers were identified in spider fecal material and found to correlate to body metal levels. Body metal dry weight concentrations of Cd, Cr, Cu, Zn and total metals in female A. trifasciata exhibited distinct patterns of spatial and annual variation during 2006 and 2007. Spider body size was homogeneous across sites in both years, while increased Cd and Cr concentrations were sometimes associated with a reduction in spider size, though the influence of Cr was quite minor. Spiders with higher body Cu levels showed a reduction in peak area for hypoxanthine and an un-identified component in fecal material chromatograms. Spatial and annual differences in metal bioaccumulation are likely mediated by variation in site-specific environmental parameters and rainfall, while the negative relationships between body size and metal levels are presumably a consequence of a spider's expenditure of energy for metal tolerance mechanisms vs. foraging and growth. Finally, correlating body metal levels with excreta products constitutes a novel method to non-invasively predict metal levels in spiders.

Aquatic subsidies transport anthropogenic nitrogen to riparian spiders

Stable nitrogen isotopic composition ( δ 15N) of aquatic biota increases with anthropogenic N inputs such as sewage and livestock waste downstream. Increase in δ 15N of riparian spiders downstream may reflect the anthropogenic pollution exposure through predation on aquatic insects. A two-source mixing model based on stable carbon isotopic composition showed the greatest dependence on aquatic insects (84%) by horizontal web-building spiders, followed by intermediate (48%) and low (31%) dependence by cursorial and vertical web-building spiders, respectively. The spider body size was negatively correlated with the dietary proportion of aquatic insects and spider δ 15N. The aquatic subsidies transported anthropogenic N to smaller riparian spiders downstream. This transport of anthropogenic N was regulated by spider’s guild designation and body size.

Silk elasticity as a potential constraint on spider body size

Silk is known for its strength and extensibility and has played a key role in the radiation of spiders. Individual spiders use different glands to produce silk types with unique sets of proteins. Most research has studied the properties of major ampullate and capture spiral silks and their ecological implications, while little is known about minor ampullate silk, the type used by those spider species studied to date for bridging displacements. A biomechanical model parameterised with available data shows that the minimum radius of silk filaments required for efficient bridging grows with the square root of the spider’s body mass, faster than the radius of minor ampullate silk filaments actually produced by spiders. Because the morphology of spiders adapted to walking along or under silk threads is ill suited for moving on a solid surface, for these species there is a negative relationship between body mass and displacement ability. As it stands, the model suggests that spiders that use silk for their displacements are prevented from attaining a large body size if they must track their resources in space. In particular, silk elasticity would favour sexual size dimorphism because males that must use bridging lines to search for females cannot grow large.

Climate change and altitudinal variation in sexual size dimorphism of arctic wolf spiders

CR Climate Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials CR 41:259-265 (2010) - DOI: https://doi.org/10.3354/cr00855 Climate change and altitudinal variation in sexual size dimorphism of arctic wolf spiders Toke Thomas Høye1,*, Jörg U. Hammel2 1Department of Wildlife Ecology and Biodiversity, National Environmental Research Institute, Aarhus University, Grenåvej 14, 8410 Rønde, Denmark 2Institute of Systematic Zoology and Evolutionary Biology with Phyletic Museum, Friedrich-Schiller-University Jena, Erbertstr. 1, 07743 Jena, Germany *Email: toh@dmu.dk ABSTRACT: Climate change is advancing the onset of the growing season, and this is happening at a particularly fast rate in the Arctic. Although this has recently been shown to affect the sexual size dimorphism (SSD) of a wolf spider species through time, it remains to be shown whether spatial variation in the physical environment is similarly affecting SSD. We studied altitudinal variation in adult body size of male and female wolf spiders on Disko Island, West Greenland. Two species exhibited female-biased SSD (measured by carapace width) at sea level but not at higher altitudes. Males and females of a third species were of equal size at both altitudes, and the 2 remaining species found on Disko Island were only present at 1 low altitude site each. Altitudinal variation in SSD is probably a result of sex differences in body size response to shorter growing seasons with altitude. Our results suggest that climate change may result in increased SSD. Constraints on body size may increase with altitude, and expanding growing seasons due to climate change may predominantly affect SSD at higher altitudes. Such intra-specific effects of climate may be widespread and suggest that further research in this topic is needed. KEY WORDS: Body size · Carapace width · Climate impacts · Intra-specific variation · Lycosidae Full text in pdf format Supplementary material PreviousCite this article as: Høye TT, Hammel JU (2010) Climate change and altitudinal variation in sexual size dimorphism of arctic wolf spiders. Clim Res 41:259-265. https://doi.org/10.3354/cr00855Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in CR Vol. 41, No. 3. Online publication date: May 04, 2010 Print ISSN: 0936-577X; Online ISSN: 1616-1572 Copyright © 2010 Inter-Research.

Body size–climate relationships of European spiders

AbstractAim Geographic body size patterns of mammals and birds can be partly understood under the framework of Bergmann’s rule. Climatic influences on body size of invertebrates, however, appear highly variable and lack a comparable, generally applicable theoretical framework. We derived predictions for body size–climate relationships for spiders from the literature and tested them using three datasets of variable spatial extent and grain.Location Europe.Methods To distinguish climate from space, we compared clines in body size within three datasets with different degrees of co‐variation between latitude and climate. These datasets were: (1) regional spider faunas from 40 European countries and large islands; (2) local spider assemblages from standardized samples in 32 habitats across Europe; and (3) local spider assemblages from Central European habitats. In the latter dataset climatic conditions were determined more by habitat type than by geographic position, and therefore this dataset provided a non‐spatial gradient of various microclimates. Spider body size was studied in relation to latitude, temperature and water availability.Results In all three datasets the mean body size of spider assemblages increased from cool/moist to warm/dry environments. This increase could be accounted for by turnover from small‐bodied to large‐bodied spider families. Body size–climate relationships within families were inconsistent.Main conclusions Starvation resistance and accelerated maturation can be ruled out as explanations for the body size clines recorded, because they predict the inverse of the observed relationship between spider body size and temperature. The relationship between body size and climate was partly independent of geographic position. Thus, the restriction of large‐bodied spiders to their glacial refugia owing to dispersal limitations can be excluded. Our results are consistent with mechanisms invoking metabolic rate, desiccation resistance and community interactions to predict a decrease in body size from warm and dry to cool and moist conditions.

Ontogenetic body-mass scaling of resting metabolic rate covaries with species-specific metabolic level and body size in spiders and snakes

According to common belief, metabolic rate usually scales with body mass to the 3/4-power, which is considered by some to be a universal law of nature. However, substantial variation in the metabolic scaling exponent ( b) exists, much of which can be related to the overall metabolic level ( L) of various taxonomic groups of organisms, as predicted by the recently proposed metabolic-level boundaries (MLB) hypothesis. Here the MLB hypothesis was tested using data for intraspecific (ontogenetic) body-mass scaling of resting metabolic rate in spiders and boid snakes. As predicted, in both animal groups b varies mostly between 2/3 and 1, and is significantly negatively related to L. L is, in turn, negatively related to species-specific body mass ( M m: estimated as the mass at the midpoint of a scaling relationship), and as a result, larger species tend to have steeper metabolic scaling slopes ( b) than smaller species. After adjusting for the effects of M m, b and L are still negatively related, though significantly only in the spiders, which exhibit a much wider range of L than the snakes. Therefore, in spiders and snakes the intraspecific scaling of metabolic rate with body mass itself scales with interspecific variation in both metabolic level and body mass.

Mass-mediated sex differences in climbing patterns support the gravity hypothesis of sexual size dimorphism

Abstract. The gravity hypothesis of sexual size dimorphism can explain the patterns of extreme sexual size dimorphism in spiders (males smaller than females) because small males climb faster and therefore may be better at reaching females that live in high habitats. Recently, the main prediction of a negative relationship between climbing speed and body size in spiders has been called into question. Here we induced males and females of the spider Leucauge venusta (Tetragnathidae) to run on vertical surfaces and found partial support for the gravity hypothesis. As predicted, males climb faster than females and we demonstrated that this effect is an indirect effect mediated by the negative relationship between body mass and climbing speed. We validate our results using simulated data showing that there is enough statistical efficiency in our data set to support our conclusions. We distinguished between direct and indirect effects (through mass) on sex differences in climbing speed by means of path analysis. Thus, we provide empirical evidence that by being smaller, males are able to climb faster than females. However, we found only a barely significant negative relationship between climbing speed and body size when only males were considered. Reasons for such results are discussed within the text.

The body size of the New Zealand orb‐weaving spider Waitkera waitakerensis (Uloboridae) is directly related to temperature and affects fecundity

Abstract. Waitkera waitakerensis occupies lowland forests of New Zealand's North Island, where temperatures decrease in a southwestward direction. The mean annual temperatures of 18 collecting sites, as extracted from GIS data, are directly related to the first femur length of adult females. Neither site elevation nor phylogeny affected spider size or other variables examined. The direct relationship between spider body size and environmental temperature followed a pattern observed in other terrestrial arthropods with a univoltine life cycle and can probably be explained by the longer growing season of warmer regions. Egg diameter was uniform across the species. Site temperature and female first femur length were each directly related to the number of eggs deposited in egg sacs. The date of egg sac collection was inversely related to egg number, suggesting that clutch size declines during the reproductive season. Females deposit eggs beneath a triangular platform and then cover them with a lower silk sheet. The area of this upper platform and the volume of the egg sac were each directly related to egg number, but not to female first femur length. The depth of the lower covering was not related to egg number or to spider first femur length. This suggests that spiders use information about the volume of eggs in their abdomens to construct an egg sac whose volume will accommodate the volume of eggs to be laid and that females do so principally by adjusting the size of the sac's upper triangular platform.

Variable dependence on detrital and grazing food webs by generalist predators: aerial insects and web spiders

Recent studies have shown that organisms from the detritus food web subsidize generalist predators in aboveground food webs, but its significance in space and time is largely unknown. Here we report seasonal dynamics of aerial insects from grazing and detritus food webs in both forest and grassland habitats, and show how these patterns influence the dependence of web spiders on the detritus food web. Detrital insects were more abundant in spring, decreased in summer, and then increased slightly in autumn. This pattern was most conspicuous in Nematocera. Due to different seasonal activity patterns of grazing and detrital insects, the proportion of detrital insects was greater in spring and autumn. Detrital insects were relatively more abundant in the forest than in the grassland. Prey captured by web spiders generally reflected seasonal and spatial patterns of aerial insect abundance. In particular, Leucauge spiders reversed their dependence on the two food webs seasonally. Body size of spiders was negatively correlated with the proportion of detrital prey, suggesting that the detrital subsidy is essential for relatively small predators. This size effect probably resulted from interaction of the following two factors: 1) the maximum body size of prey that can be caught increased with spider body size, 2) larger body size classes of aerial insects included a higher proportion of insects from the grazing food web.

Experimental competition release in a community of web‐weaving spiders

Spiders are generalist predators, abundant in terrestrial ecosystems, and hence good candidates for interspecific competitive constraints. Contrary to these premises, evidence of interspecific competition in web‐weaving spiders is ambiguous, and new experiments on natural communities are interesting. This paper reports on an experiment designed to test competitive effects in a natural community of web‐weaving spiders, accomplished by selective removal of each of the three locally dominant species: Araneus marmoreus, Argiope bruennichi, and Agelena labyrinthi‐ca. No statistically significant difference was found among control plots and the plots where one of the three species had been removed, for any of the variables measured, but the small number of replicates limited statistic power. Considering only effect direction, and not statistical significance, these removal experiments supported competitive effects on community structure, habitat overlap, and spider body size. On the other hand, effects were contrary to competitive expectations as regards abundance and habitat breadth. These results are in line with the findings of the other removal experiments conducted so far on spiders, that uncovered small intra‐ and interspecific competitive effects for some variables but not for others. So far, there is no evidence that interspecific competition may affect spider communities, although a low‐level competition remains possible, but difficult to test statistically for its evolutionary consequence.

Negative effects of ant foraging on spiders in Douglas-fir canopies

Spiders and ants are potential competitors and mutual predators. Indirect evidence from previous research has suggested that ant foraging may significantly lower the abundance of arboreal spiders in young Douglas-fir plantations in western Oregon. This study tested the effect of foraging by ants, dominated by Camponotus spp., on spider assemblages in Douglas-fir canopies in a 5-month ant-exclusion experiment. The biomass of potential prey organisms on foliage, dominated by Psocoptera, increased significantly by 1.9- to 2.4-fold following ant exclusion. The removal of ants did not affect the abundance of flying arthropods in the vicinity of tree canopies as indicated by sticky trap catches. The abundance of hunting spiders, the majority being Salticidae, increased significantly by 1.5- to 1.8-fold in trees without ants in the late summer; neither the abundance of web-building spiders nor the average body size of hunting and web-building spiders were significantly affected by ant removal. Spider diversity and community structure did not differ significantly between control and ant-removal trees. The majority of prey captured by ants were Aphidoidea (48.1%) and Psocoptera (12.5%); spiders represented only 1.4% of the ants' diet. About 40% of observed ants were tending Cinara spp. aphids. Our observations suggest that the lower abundance of hunting spiders in control canopies with ants may be due to interference competition with ants resulting from ant foraging and aphid-tending activities. Direct predation of spiders by ants appeared to be of minor importance in this study system. This study did not provide sufficient evidence for exploitative competition for prey between ants and spiders.

アリを専食するミジングモ属（Ｄｉｐｏｅｎａ）３種の餌構成

We examined species and size compositions of prey in the three Dipoena spiders specializing on ants. Dipoena punctisparsa fed exclusively on small ants, Lasius. In this spider, the number of prey fed at a time increased with the spider body size. Dipoena castrata mainly captured Componotus and Lasius, and most spiders fed on a single prey. The body size of prey fed upon by this species increased with the spider size. Dipoena mustelina captured a variety of ant species, ranging from very small to large ones.